At least six people were killed and dozens wounded when grenades exploded in towns in eastern and western Ethiopia, the latest in a string of mystery blasts in the country, police said on Thursday.

Grenades were detonated at two bars and a church in the remote eastern town of Jijiga on Saturday evening, killing at least three people and injuring between 11 and 23 people, according to police and an aid worker there.

On Sunday, another grenade exploded in a market in the western town of Gedo, killing three people and wounding about 30, police said.

The explosions in Jijiga, about 700km east of the capital, Addis Ababa, appeared to be coordinated attacks and were set off at the same time, about 7.30pm local time on Saturday, police in the capital said.

"Two hand grenades exploded in two different local bars [and] another exploded in a small Protestant church around that time," a senior officer said on condition of anonymity. He said the number of injuries was not clear.

But an aid worker in Jijiga, who said the blasts occurred between 7.30pm and 8 pm, said that as many as 23 people were injured. "It's between 11 and 23, depending on who you talk to," the worker said.

In Gedo, about 150km west of Addis Ababa, the grenade ripped through a crowded market on Sunday afternoon, killing three people and injuring about 30, the police official said.

Further details of the explosions in Jijiga and Gedo were not immediately available, but police said they were investigating to see who may have been behind the blasts.

Increase

Ethiopia has seen an increase in such incidents in recent months. Since the beginning of the year, Addis Ababa has been hit by at least 11 explosions, some attributed to grenades and others to landmines.

On April 6, a small device -- believed to be a mine -- was detonated outside the headquarters of Ethiopia's coffee-export offices, causing minor damage. The blast came shortly after authorities defused a bomb at the capital's train station.

In late March, one person was killed and 15 others wounded when five separate devices were detonated in the capital, including one on a minibus and one in a restaurant.

Earlier in March, three grenades exploded in Addis Ababa, injuring four people, and in January two grenades were thrown at a bank and a hospital in the capital, causing some damage but no injuries.

No one has claimed responsibility for the blasts, but various authorities have identified the most likely culprits as being separatist rebels, Somali Muslim extremists, opposition groups or Ethiopia's arch-rival neighbour Eritrea.

The two countries fought a war over their common border from 1998 to 2000 that cost at least 80 000 lives and tensions remain acute.

Tension has also been high in Addis Ababa since the deaths in June and November 2005 of at least 84 people -- many at the hands of police -- during opposition-led protests against alleged fraud in the disputed May 2005 election.

The government has accused opposition leaders, many of whom are now on trial for conspiracy, of trying to foment a coup d'état.

Late on Wednesday, the Ethiopian federal police mounted a citywide campaign searching vehicles for weapons and ammunition, witnesses said. --